When it comes to having sex, there are nuggets of so-called wisdom most of take as gospel. Those with dodgy hearts or bad backs for example, should avoid sex or take it easy, women on their period can’t get pregnant and peeing beforehand could reduce the risk of a urinary tract infection. As it turns out, most such nuggets are nothing but myths.

Someone will happen to have a heart attack at the same time as they’re having sexual intercourse and those are the cases we hear about, says Dr Mark Knapton, associate medical director of the British Heart Foundation. ‘But they were going to have a heart attack anyway, it’s not the sex that did it.’

‘What’s more worrying is when patients experience erectile dysfunction as this is often a sign of an underlying heart problem,’ added Dr Knapton.

The same rules don’t apply if to the adulterous, however.

A paper published in 2012 in The Journal of Sexual Medicine found men were more likely to experience ‘sudden coital death’ – a fatal heart attack during sex – during sex with someone other than their wives.

‘Sex causes arousal, excitement, stimulation of the adrenal glands,’ says Dr Knapton, adding that these effects may be heightened with a new partner.

‘It’s a bit like the excitement of watching a football match, which has also been reported to lead to increased numbers of calls to health emergency services because of cardiac problems.

Those with significant heart failure, damage to their heart muscle or a history of severe angina might experience breathlessness that could limit their sexual activity, and should talk to their doctors.

Sexual activity can in fact, count as an essential part of the 30 minutes a day exercise regime of heart attack patients, Dr Knapton advises. But only if it lasts that long – which is unlikely, he says.

Indeed, a paper published in January 2013 in the New England Journal of Medicine examined the body of evidence for the claim that sex is good exercise and concluded that the average bout of sexual activity was only six minutes and expended a paltry 21 calories.

#2 If you stand on your head after sex it increases your chances of getting pregnant: MYTH

In fact, lying down instead is more effective at increasing your chances of pregnancy.

A randomised controlled trial published in the British Medical Journal in 2009 looked at 400 couples who were being artificially inseminated and found that the women that lay flat for 15 minutes had a 50 per cent greater chance of getting pregnant than those that immediately got up and walked around.

The same may hold true when comes to getting pregnant after having sex, says Dr Gabrielle Downey, consultant gynaecologist and obstetrician at BMI Hospital, The Priory in Birmingham.

But while there’s absolutely no need to stand on your head, you can help the process along.

‘A woman’s uterus is bent slightly forwards so if you tilt your pelvis upward a little, say by putting a pillow under your lower back as you lie down, the sperm will have less of a distance to travel,’ says Dr Downey.

‘That means they are effectively travelling downhill and need less energy to get to where they want to go.’

But why 15 minutes? Post-sex sperm have to get into the womb, travel across it and through the fallopian tubes, she explains.

‘I would actually suggest that lying down for half an hour after sex would be better, to ensure this process has enough time to happen,’ advises Dr Downey.

After that, gravity isn’t quite so important to sperm’s movements as the fallopian tubes have rhythmical movements within them that help the movement of sperm along, she explains.

#3 You can’t get pregnant on your period: MYTH

There is no time at which a woman between the ages of 15 and 50 can’t get pregnant, says Dr Gillian Lockwood, consultant obstetrician and gynaecologist and medical director of Midland’s Fertility Services.

Ideally, the window of opportunity for implantation when conception can occur, is a brief three to four day time which occurs round about cycle days 18 or 19, taking cycle day one as the first day of the period, she says.

But a good egg released during ovulation has a life span of possibly about four or five days days and healthy sperm have fertilising capacity for up to four days, she asserts.

‘This is why we hear about lots of women who’ve thought, ‘Oh, it’s the tail end of my period. I’m perfectly safe”, but actually, they get pregnant.’

Furthermore, according to Dr Gabrielle Downey, post-pregnancy you might be at increased risk.

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During pregnancy, all your hormone levels are high generally, except the ones that stimulate your ovaries to make eggs are low, she explains. But this changes.

‘After you have had the baby, the brain tries to stimulate the ovaries again to make eggs so it can induce another pregnancy, so it sends out strong hormonal signals to the eggs to say ‘Right. Start working,’’ she says.

‘The effect is so strong that it’s almost like having fertility treatment so don’t use having your period as contraception.’

#4 Headaches are a good excuse not to indulge: MYTH (…and sex might help)

In women, orgasm might actually help the pain of a headache cancelling out the age-old ‘Not tonight darling…’ excuse.

In fact, in research published in 2013, a team of neurologists from the University of Munster, Germany found that over half of migraine sufferers who had sex during an episode experienced an improvement in symptoms.

Staggeringly, one of five finished with no pain at all – a difference seen in male sufferers in particular.

The researchers theorised that sex triggered the release of endorphins, the body’s natural painkillers, through the central nervous system, which could reduce or eliminate a headache.

Indeed, according to Dr Beverley Whipple, the neurophysicist from Rutgers Universitywho discovered the G-spot in the late 70s (on the front wall of the vagina, 5cm from the entrance), having this area stimulated to orgasm increased women’s pain threshold by 106 per cent.

#5 People with bad backs should avoid strenuous sex: MYTH

A staggering four out of five people experience at least one episode of debilitating low back pain in their lifetimes and up to 84 per cent of men and 73 per cent of women with the condition report a decrease in the frequency of sex.

But research published in October last year in the journal Spine found that certain positions could make sex less painful for sufferers – depending on the type of back pain you have.

Women who get low back pain when they arch their backs or lie on their stomachs experienced less pain in the missionary position, the researchers found.

For men with back pain (especially if it hurt when they touched their toes or sat for too long), doggy style was the best position and adopting a ‘hip-hinging motion instead of thrusting with their spines’ could also lessen the pain.

According to physiotherapist Tim Allardyce of Surrey Physio, doggy style is indeed a good position for low back pain in men – with one caveat.

‘They have to ensure they are on their knees rather than standing up,’ he explains.

‘One of the biggest causes of pain for lower back pain sufferers or those with slipped discs is forward bending,’ he says.

‘By kneeling the back remains in a safe position, maintaining its natural curve which will minimise the pain during sex.’

If the man is standing on the other hand (with the woman on all fours on the bed) he will often have to bend his knees a little, round his back and lean forward to get the right angle, Allardyce says. This can increase low back pain or strain an existing injury.

He agrees that the missionary is good for women with lower back pain as it keeps her spine on neutral, that is, in a slight S-shaped from the lower to upper spine, thus minimising pain or further injury.

Kneeling during doggy style or woman on top may also work for women – as long as she doesn’t arch her back too much.

‘The main thing is to keep that natural curve in the spine and not round or arch.’

What women should avoid is bending fully forwards with the man behind them, as this puts too much strain on the lower discs of the spine and may lead to injury, says Allardyce.

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While there’s no reason those with back pain need to avoid having sex, some things are just asking for trouble, he asserts.

‘When people start doing like having sex over sofas or in cars and showers, they often need to get their bodies into tight, complicated environments and find themselves aggravating an existing back problem or creating a whole new one,’ he warns.

So what’s the most back-unfriendly sex move? ‘Definitely a man trying to pick someone up – literally – against a wall, in the shower or into mid-air,’ says Allardyce.

#6 If you pee before sex you reduce your chances of an STI: MYTH

Around half of all women and one in 2000 men will develop a urinary tract infection (UTI) each year, according to the NHS.

UTIs develop when the bladder becomes infected, usually by bacteria which most commonly enter through the urethra.

Sex is a common cause of UTIs in young women in their 20s, says Dr Zaki Almallah, consultant urologist at BMI Hospital in Edgbaston.

But it also affects older women. One study in 2008 published in the Journal of General Internal Medicine also found that sexual intercourse was also associated with the risk of UTI in postmenopausal women too.

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While most of us are told to pee before and after sex to avoid UTIs, this is only half true, say experts.

Indeed, according one leading New York urologist Dr David Kaufman, peeing before sex ‘is the number one cause of post-coital urinary tract infections.’

According to Kaufman, UTIs can be caused when during sex, bacteria can get pushed into the urethra. But not urinating before sex means you will have enough stored in the bladder to create a strong stream, making it more likely that bacteria will be flushed.

While Mr Almallah says there’s no real evidence for Dr Kaufman’s theory, he says there is no need to urinate before sex if you don’t need to, as it will have no effect on preventing a post-intercourse UTI. But urinating afterwards can help.

Bacteria that cause UTIs usually live naturally in the area called the perineum – between the anus, vagina and urethra – and sex can transport bacteria from these areas into the bladder through the pipe of the urethra.

‘Urinating after sex means you’re flushing out any bacteria that has lodged during intercourse into the urethra, which is the source of this transport of bacteria into the bladder, thus helping minimise your chances of a post-sex UIT,’ Mr Almallah explains.

#7 Sex and orgasm can induce early labour: MYTH

Theoretically, sex can induce labour, but the cervix needs to be ready, explains Dr Downey. Semen contains hormones called prostaglandins (which come from the man’s prostate gland) which can soften the cervix and stimulate contractions.

Synthetic forms of these are used medically to induce labour, which is why – theoretically – it’s possible that sex may hasten labour. But only if you’re close to your due date.

‘Your cervix has to ripen and be receptive to prostaglandins and this only happens near the end of your pregnancy,’ Dr Downey says. ‘If your cervix isn’t ready, having sex at 20 weeks won’t make you go into early labour.’

Having said that, sex may induce Braxton Hicks contractions, caused by the pain from tightening of the uterine muscles felt often in the second or third trimester and sometimes mistaken for labour pains.

‘Anything that stimulates movement in the uterus can cause Braxton Hicks – including sex – but the difference will be that they tend to only last 20-30 seconds and will rarely stop you from doing what you’re doing, which is a tell tale sign you’re in labour’.

Plus, real labour pains start and get progressively worse and more frequent, while Braxton Hicks tend to be short-lived, she explains.

There are caveats however.

If your midwife or consultant have said your membranes have ruptured (when a tear develops in the fluid-filled bag that surrounds the baby), if you have low-lying placenta (usually detectable at your 20 week scan), if you are having twins, are at increased risk of infection or expecting a premature baby, you may be advised to avoid sex during part or all of you pregnancy, Dr Downey explains.